This invention relates generally to gas turbine engines and more particularly to counter-rotating turbines for gas turbine engines.
A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and ignited for generating hot combustion gases. These gases flow downstream to one or more turbines that extract energy therefrom to power the compressor and provide useful work such as powering an aircraft in flight. In a turbofan engine, which typically includes a fan placed at the front of the core engine, a high pressure turbine powers the compressor of the core engine. A low pressure turbine is disposed downstream from the high pressure turbine for powering the fan.
In one type of turbofan engine, a counter-rotating low pressure turbine is provided downstream of the core engine for driving forward and aft counter-rotating fan rotors. Each of the counter-rotating turbine rotors includes a plurality of turbine blades extending therefrom in predetermined numbers of axial stages.
The components of the counter-rotating turbine must be able to withstand the high temperature environment in which they operate. This often requires that they be cooled, for example with relatively cooler air flow extracted from an upstream location in the engine. A satisfactory turbine cooling system must be tolerant of several factors which may cause deviations from the design condition. These factors include the possibility of a broken cooling air delivery pipe or failed sealing components, the effect of manufacturing tolerances, engine maneuvers and resultant impact on seal clearances, and cavity purge requirements to prevent flowpath ingestion.
Accordingly, there is a need for a counter rotating turbine having robust sealing and cooling provisions.